Silicided semiconductor structure and method of forming the same

ABSTRACT

A preferred embodiment includes a method of manufacturing a fuse element that includes forming a polysilicon layer over a semiconductor structure, doping the polysilicon layer with carbon or nitrogen, depositing a metal over the polysilicon layer; and annealing the metal and polysilicon layer to form a silicide in an upper portion of the polysilicon layer.

TECHNICAL FIELD

The present invention relates generally to semiconductor devices and methods and, in a particular embodiment, to a silicided semiconductor structure and a method of forming the same.

BACKGROUND

Fuse elements, such as fuse links and program transistors, are programmable electronic devices that are employed in a wide variety of semiconductor applications. For example fuse links and program transistors may be employed to enable redundant memory cells in a memory array, to program a chip identification, or to customize integrated circuits after production.

A fuse is normally closed or linked. Programming the fuse means opening or blowing a fuse link located in the fuse, which results in a significant increase in resistance. In contrast an anti-fuse is normally open, e.g., the fuse has a capacitor like structure. Programming the anti-fuse means closing the capacitor like structure of the anti-fuse which results in a short or decrease in resistance.

There are several different types of fuses and anti-fuses. One type of conventional fuse includes an electrically programmable fuse. This electrically programmable fuse may include a polysilicon/silicide stack. The polysilicon/silicide stack typically includes polycrystalline silicon and an overlayer of silicide.

SUMMARY OF THE INVENTION

In accordance with a preferred embodiment, the present invention includes a method of forming a semiconductor device. The method of manufacturing a fuse element comprises forming a polysilicon layer over a semiconductor structure, doping the polysilicon layer with carbon or nitrogen, depositing a metal over the doped polysilicon layer; and annealing the metal and polysilicon layer to form a silicide in an upper portion of the polysilicon layer.

The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects and advantages of the invention will be apparent from the description, the drawings and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

FIG. 1 shows a detailed view of a top portion of a polysilicon structure;

FIG. 2 shows a cross sectional view of a semiconductor device separated in a first region and a second region;

FIGS. 3 a and 3 b provide a cross sectional view of two preferred embodiments of the semiconductor device;

FIG. 4 a shows a cross sectional view of the semiconductor device, wherein a first region comprises a transistor and a second region comprises a fuse element;

FIG. 4 b provides a top view of the semiconductor device, wherein a first region comprises a transistor and a second region comprises a fuse element;

FIG. 5 and FIG. 6 show cross sectional views of the semiconductor device at various stages of manufacturing in accordance with a preferred embodiment of the present invention, wherein a polysilicon is formed, doped and formed over the fuse element; and

FIG. 7 shows a cross sectional view of a semiconductor device in accordance with a preferred embodiment of the present invention, wherein the gate polysilicon of the transistor and the polysilicon of the fuse element are silicided.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the presently preferred embodiments are discussed in detail below. It should be appreciated, however, that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use the invention, and do not limit the scope of the invention.

The present invention will be described with respect to preferred embodiments in a specific context, namely a semiconductor device including a fuse element and a method to manufacture a semiconductor device, especially a fuse element. FIG. 1 shows an example structure while FIGS. 2 through 7 show cross sectional views of a semiconductor device 100 at various stages of manufacturing in accordance with a preferred embodiment of the present invention.

FIG. 1 provides a first example of a structure that utilizes aspects of the present invention. In particular, this view shows a first region 101 and a second region 102 of a semiconductor device that includes a first structure 220 and a second structure 230. In this embodiment, a polysilicon layer 203 has been processed to form a first polysilicon structure 203 a and a second polysilicon structure 203 b over a workpiece, which can include any type of substrate, such as a semiconductor wafer or other. A silicide layer 208 is formed so that first silicide structure 208 a overlies the first polysilicon structure and a second silicide structure 208 b overlies the second polysilicon structure 203 b. Preferably, the thickness of the first silicide structure 208 a is greater than the thickness of the second silicide structure 208 b. In one example, the first silicide structure entirely consumes the underlying polysilicon while the second silicide structure does not.

In one example, as will be discussed in greater detail below, the first structure 220 is the gate of a transistor while the second structure 230 is a fuse element. In fuse technology, it is important that a sufficient thickness of polysilicon be retained to ensure that the fuse will operate properly. This is especially important in smaller technology nodes. For example, in order to continue using a polysilicon fuse at feature sizes of 32 nm and below, some innovation is needed to avoid fully siliciding the polysilicon when the polysilicon thickness is reduced to 500 Å or below.

In one embodiment, the desired structure can be obtained by performing a special doping into the polysilicon in the eFuse area to control the final silicide thickness and properties. This doping can slow down the silicidation rate to avoid the fully silicided issue. As will be shown, the special doping can be tailored to have no impact on other areas of a chip, including a logic device, SRAM cells and resistor structures. In fact, it is possible to change the property of silicide for easy electro-migration without adversely affecting other structures.

In view of the processing, the silicidation rate at the first polysilicon layer 203 a in the first region 220 is different than the silicidation rate of the second polysilicon layer 203 b in the second region 230. The dopants, for example, carbon or nitrogen, slow down the silicidation rate at the second polysilicon layer 203 b resulting in a different thickness of the silicide layer 208 over the first polysilicon layer 203 a at the transistor 220 than over the second polysilicon layer 203 b over the fuse element 230. Accordingly, the silicide formation may consume more polysilicon in the polysilicon layer 203 of the transistor 220 than the in the polysilicon layer 203 of the fuse element 230.

In various embodiments, the ratio of the silicide thickness for the thicker silicide to the silicide thickness for the thinner silicide may be greater than 1.1, e.g., a range from about 1.1 to about 1.5. In another embodiment, the ratio is greater than 1.2. The ration of the polysilicon vs. silicide for the transistor and polysilicon vs. silicide for the fuse will depend upon the technology node. For example, for 32 nm and 60 nm technology nodes, the ratio of polysilicon vs. silicide for the transistor is about 1.18 and 0.85 for the ratio polysilicon vs. silicide for the fuse.

A preferred embodiment method will now be described with respect to FIGS. 2-7. FIG. 2 shows a semiconductor body 100, which has a first region 101 and a second region 102. The semiconductor body 100 may include a semiconductor substrate 200 which may include bulk silicon, silicon on insulator (SOI), compound semiconductors such as GaAs, InP, Si/Ge or SiC or any other suitable material.

Isolation regions 210 are formed within the semiconductor substrate 200. The isolation regions 210 provide electrical isolations between various regions of the semiconductor substrate 200. In one embodiment, the isolation regions are typically shallow trench isolations (STI), or isolation trenches (TI). In an alternate embodiment, field oxide or deep trench isolation can be used, as just two examples.

A dielectric layer 201 is formed overlying the semiconductor substrate 200. The dielectric layer may include traditional insulating materials used for gate dielectrics, such as silicon dioxide (SiO₂), silicon nitride (Si_(x)N_(y)) or silicon oxynitride (SiON) or a combination of. However, embodiments of the present invention may also, or alternatively, use high-k materials with a dielectric constant of about 15 or greater. Thus, the dielectric layer 201 may include HfO₂, HfSiOx, Al₂O₃, ZrO₂, Si_(x)N_(y), SiON, as examples. The dielectric layer 201 may comprise a single layer of material, or alternatively, two or more layers. The dielectric layer 201 may be formed by chemical vapor deposition (CVD), atomic layer deposition (ALD), metal organic chemical vapor deposition (MOCVD), physical vapor deposition (PVD), or jet vapor deposition (JVD), as examples, although alternatively, the dielectric layer 201 may be formed using other techniques. The dielectric layer preferably includes a thickness of about 50 Angstroms or less in one embodiment, although alternatively, the dielectric layer 201 may include other dimensions, such as about 80 Angstroms or less. The dielectric layer 201 preferably includes about 20 to 30 Angstroms physical thickness.

A conductive layer 202 overlies the dielectric layer 201. The conductive layer 202 may include doped silicon, Ti, TiN, Ta, or TaN. Alternatively, the conductive layer may include other metal materials. The conductive layer 202 is preferably deposited using MOCVD in one embodiment, although alternatively, the conductive layer 202 may be formed by ALD, PVD or other deposition techniques. This is an optional step that is not required in embodiments of the present invention but may be appropriate for some transistor designs.

FIG. 3 a illustrates an embodiment of a semiconductor device 100. An opening 204 is formed into the conductive layer 202 and, optionally, into the dielectric layer 201 in the second region 102 of the semiconductor device 100. The opening 204 is formed by an etch process, for example, a dry etch or, alternatively, by a wet etch. In a preferred embodiment the etch process removes the conductive layer 202. Alternatively, the etch process may remove the conductive layer 202 and the dielectric layer 201.

A polysilicon layer 203 is then deposited over the conductive layer 202 and the opening 204, filling the opening. The polysilicon layer 203 is preferably deposited by a chemical vapor deposition (CVD) process. The polysilicon layer 203 preferably includes a thickness of about 600 Angstroms or less in one embodiment, although alternatively, the polysilicon layer 203 may include other dimensions, such as about 500 Angstroms or less. In other embodiments, the polysilicon layer 203 preferably has a thickness from about 200 to 800 Angstroms.

Referring now to FIG. 3 b, in an alternate embodiment, an opening 204 is formed into the conductive layer 202, the dielectric layer 201 and the isolation region 210 in the second region 102 of the semiconductor device 100. The opening 204 is formed by an etch process and followed by an optional deposition of a dielectric layer, not shown, on the bottom and the sidewalls of the opening 204. The dielectric layer may include silicon dioxide (SiO₂), silicon nitride (Si_(x)N_(y)), silicon oxynitride (SiON) or any other suitable material. Polysilicon is then deposited over the conductive layer 202 and the optional dielectric layer, filling the opening, and forming a polysilicon layer 203.

FIG. 4 a illustrates a cross sectional view of the semiconductor substrate 200 after further processing. A transistor 220 is formed between isolation region 210 in the first region 101 and may include a first and second source/drain region 221, 222, a channel region 224 between the first and second source/drain region 221, 222, a gate dielectric 201 overlying the channel region 224, a metal layer 202 overlying the gate dielectric 201, and a polysilicon gate 203 overlying the metal layer 202. Spacers 225 may be formed on either side of the transistor stack. A fuse element 230 is formed in the second region 102 and may include an isolation layer 201 beneath polysilicon layer 203. At the opposite ends spacers 226 may be formed.

The transistor 220 and the fuse element 230 are formed using traditional depositing, patterning, etching and removing techniques. By using these techniques, in one embodiment, the conductive layer 202 is completely removed in the first region 101. In another embodiment, the polysilicon layer 203 is disposed over the conductive layer 202 and both layers form a gate region for a transistor.

For example, a mask, e.g., photoresist can be formed over the wafer. The mask can then be patterned photolithographically to form the transistor gates (one is shown in the figure) and the fuses (again only one is shown). An example of a pattern of the gate conductor and fuse is shown in FIG. 4 b, which illustrates a top view of the cross section of FIG. 4 a. The fuse element 230 may include an anode 231, a cathode 232 and a fuse link 233. In a preferred embodiment, the anode 231, the cathode 232, and the fuse link 233 may all be from the same material. In other preferred embodiments, the anode 231, the cathode 232 may be from a different material than the anode 231 and the fuse link 233. Alternatively, other material combinations are possible.

Standard CMOS processing can then be performed to form the transistor. Lightly doped source/drain regions are formed by doping the exposed portions of source/drain regions 221, 222. Sidewall spacers can then be formed adjacent the gate, e.g., by conformal deposition of an insulating material (e.g., an oxide, nitride or combination of oxide and nitride) followed by anisotropic etching. The source/drain regions can then be completed by ion implantation and activation.

While FIGS. 4 a and 4 b provide one example of a resulting structure, it is understood that various options are available. For example, the metal portion 202 of the gate can be eliminated so that a polysilicon gate structure is included. Also various shapes and configurations for the various components can be used.

Referring now to FIG. 5, processing of the semiconductor device 200 is continued. A mask 205 is formed over the transistor 220 and the fuse element 230. The mask 205 is preferably photoresist but may also be a hard mask such as boron-doped silicon glass (BSG), tetraethoxysilane (TEOS), as examples. The mask 205 may be patterned using traditional lithography techniques. An opening 206 is formed into the mask 205 in the second region 102 above the fuse element 230. The opening exposes at least parts of the polysilicon layer 203 of the fuse link 233 and preferably the whole area of fuse element 230 including fuse link 233, anode 231, and cathode 232).

In a preferred embodiment dopants 209 may be introduced into the polysilicon 203. Typical dopants may be carbon or nitrogen. Alternatively, germanium can be used. The dopants form a dopant concentration in the upper part of the polysilicon 203. The implantation is performed at an energy level of about 5 to 20 keV and at an implantation dose of about 10¹⁰ to about 10¹³ dopants/cm², as examples. Dopant concentration and distribution in the polysilicon 203 depend on the energy level and the duration of the doping process. In another embodiment, the implantation of the dopants may be performed under an angle so that the dopant concentration at the side walls of the fuse link 233 is higher than in the middle part of the upper area of the link. As described in more detail below, the doping of the polysilicon in the second region 102 may control the final silicide thickness and the property of the fuse element 230. Selective doping of only parts of the fuse link 233, for example, can also change the property of the fuse element 230 so that electro migration issues are eased.

In FIG. 6 the mask 205 is removed from the semiconductor substrate 200. Next, in a preferred embodiment, a siliciding metal layer 207 is deposited over the polysilicon layer 203 of the transistor 220 in the first region 101 and the polysilicon layer 203 of the fuse element 230 in the second region 102 as well as the source/drain regions 221, 222. In the preferred embodiment, a self-aligned silicide or salicide process is used so the siliciding metal is blanket deposited over the entire wafer. The metal may include Ti, Ta, Pd, Cu, Ni, Pt, preferably Ni and Pt.

Then the semiconductor device 100 is annealed so that the siliciding metal layer 207 and the polysilicon layer 203 form a silicide layer 208 as can be seen in FIG. 7. In one embodiment the annealing step is performed with a low temperature annealing process. The temperatures are preferable between about 300° C. and 500° C. The low temperature process is typically carried out for about 20 minutes. In another embodiment the annealing step is performed with a high temperature annealing process. The temperatures for a high temperature annealing process are preferably between about 400° C. and 600° C. The high temperature process is typically carried out for about ten minutes.

By controlling the foregoing parameters, doping the polysilicon, depositing a siliciding metal and annealing the doped polysilicon/siliciding metal stack, the properties of the resulting silicide can be changed for different layouts of the fuse element 230 to provide easy electro-migration.

It should be noted that in a further embodiment the semiconductor device may include a memory, a capacitor, a MEMS or any other semiconductor devices.

Advantages of the preferred embodiments of the present invention include providing functional fuse elements for processing nodes smaller than 65 nm while process simplicity is ensured. The doping of the polysilicon with appropriate dopants may ensure that silicidation at the fuse element is slow, which in turn may prevent the fuse element and especially the fuse link from becoming fully silicided.

A further advantage is process economy. The doping of the fuse element adds just one additional step to the process work flow providing cost advantages for integrating fuse links into semiconductor devices.

While this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. It is therefore intended that the appended claims encompass any such modifications or embodiments.

Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps. 

What is claimed is:
 1. A method of manufacturing a semiconductor device, the method comprising: forming a polysilicon layer; doping the polysilicon layer with carbon or nitrogen; patterning the polysilicon layer to form a fuse element; forming a metal layer prior to forming the polysilicon layer, the metal layer being removed from a region of the fuse element; patterning the polysilicon layer to form a transistor gate, the transistor gate being spaced from the fuse element; depositing a metal over the polysilicon layer; and annealing the metal and the polysilicon layer to form a silicide region in an upper portion of the polysilicon layer.
 2. The method of claim 1, wherein depositing the metal over the polysilicon layer comprises depositing the metal over the fuse element and over the transistor gate, and wherein annealing forms a silicide region of a first thickness of the fuse element and a silicide region of a second thickness over the transistor gate, the first thickness being smaller than the second thickness.
 3. The method of claim 2, wherein the second thickness is substantially the same as a thickness of the transistor gate thereby forming a fully silicided gate.
 4. The method of claim 1, wherein the doping comprises ion implantation at an energy level of about 5 keV to 20 keV and an implantation dose of about 10¹⁰ dopants/cm² to 10¹³ dopants/cm². 